Equipment for measuring and displaying the time lapse between a given heartbeat and the corresponding arterial pulse

ABSTRACT

An apparatus for measuring the time interval between a heartbeat detected by an electrocardiographic detecting system and the corresponding peripheral pulse detected by a pulse sensing system is disclosed. Further features include a battery supply with a charging circuit and battery condition indicating means and a capacitor-type sample and hold circuit with constant current charging means and meter readout calibrated in pulse propagation time.

United States Patent 1191 Phelps, Sr.

1 1 3,734,086 14 1 May 22,1973

[54] EQUIPMENT FOR MEASURING AND DISPLAYING THE TIME LAPSE BETWEEN AGIVEN HEARTBEAT AND THE CORRESPONDING ARTERIAL PULSE Inventor:

[76] Jerry Allan Phelps, Sr., 6013 lnnes Trace Road, Louisville, Ky.40222 Filed: Mar. 24, 1971 Appl. No.: 127,573

US. Cl. .....128/2.06 R, 128/2.05 P, 128/2.05 T, 128/2.06 F

Int. Cl. ..A6lb 5/04 Field of Search ..128/2.05 P, 2.05 E, 128/2.05 R,2.05 T, 2.06 A, 2.06 B, 2.06 F, 2.06 G, 2.05 A

[56] References Cited UNITED STATES PATENTS 3,154,066 /1964 Grindheim eta1. ..128/2.05 P

3,090,377 5/1963 Salisbury et a1 ..l28/2.05 E 3,228,391 1/1966 Fitter etal. 1 ..128/2,05 T 3,602,222 8/1971 Hemdon .....128/2.06 F 3,613,67010/1971 Edenhofer.... .....l28/2.06 F 3,463,143 8/1969 Karsh ..128/2.06A 3,132,643 5/1964 Baum et al ..l28/2.05 A

Primary ExaminerWilliam E. Kamm Att0rney-Arthur F. Robert {57] ABSTRACT1 Claim, 2 Drawing Figures I A TIRLIHER i HERTZ gagg m AND so HERTz LowPAS-S 13 FILTER FILTER 32 [7 METER EXTERNAL PERIPHERAL PROTECTIVE PULSEINPUT c1Rcu1T 3h 33 so) F|E|) D+ 34 35x 36 METER gfigggm SAMPLE EFFECT1101.0 2553: 2? CALIBRATE QE QE SOURCE cAPAc1ToR TRANSISTOR CAPACITORBUFFER ADJUSTMENT PROPIGATM sw1Tc1-1 TIME 27 28 24 AMPLIFIER asKILOHERTZ MONO T BLE AND so HERTz BANDPASS MULTISVIQRATO 2O FILTERFILTER R 21 v v as,

EXTERNAL ELECTROCARDIOGRAM 2a INPUT 38 39 23 METER BATTERY 1 '1 READOUTCHARGE +12 VOLT e VOLT 0F BATTERY INDICATOR BATTERY BATTERY CHARGECIRCUIT BATTERY RECHARGI NG CIRCUIT PATEmmlmezlera E.C.G. GAIN sum 2 OF2 FIG. 2

\SECONDS EXTERNAL EXTERNAL E.C.G, PULSE HOURS RECHARGE PULSE GAIN OFF ONNTOR.

EQUIPMENT FOR MEASURING AND DISPLAYING THE TIME LAPSE BETWEEN A GIVENHEARTBEAT AND THE CORRESPONDING ARTERIAL PULSE BACKGROUND OF THEINVENTION A real time indication of cardiac activity, vascular status,and blood flow is very helpful in monitoring the status of a patient.This may be in regard to the clinical evaluation of a disease, themonitoring of an ill patient, or in any area where an indication of thecardiovascular integrity is deemed important.

The electrocardiogram (E.C.G.), commonly displayed or recorded in illpatients or during operations, does not give any indication of tissueblood flow other than in the heart itself; in fact, peripheralcirculation may be absent in the presence of a normal electrocardiogram.

Many other signs of vascular decompensation are now monitored, i.e.,blood pressure and pulse rate, but these parameters may only be abnormalwhen damage has already been done, or may not be as early a warning ofimpending difficulty as previously thought. During an anesthetic thepulse propigation time from the heart to an extremity, typically afinger or toe, is prolonged prior to any change in the blood pressure,pulse rate or electrocardiogram. In other words, prolongation of thepulse propigation time from the heart to a finger or toe provides anearlier warning of cardiovascular depression to a degree never possiblebefore.

There are instruments to display the blood flow through an artery, butthese require surgical procedures to attach the sensors directly to theartery, and these instruments indicate blood flow only in a segment of aparticular artery.

To the present, there has been no instrument to detect, determine, anddisplay the pulse propigation time from the heart to an extremity,typically a finger or toe, and to do this by noninvasive means.

As previously mentioned, the blood flow in a segment of a particularartery can be determined, but the attachment of the sensors requiressurgery, surgical skill, and knowledge. The present invention usesnoninvasive means to determine the pulse propigation time, requiringonly: 1.) strapping the peripheral pulse detector on a finger or toe,and, 2.) cleansing of the skin and taping the electrocardiogramelectrodes to the arms. This may be done by persons without any specialtraining, skill, or knowledge.

Because of the currently recognized hazards of electrocution or cardiacarrest during the use of high A.C. voltage equipment, especially inpatients with internal cardiac electrodes, the present invention isbattery powered.

SUMMARY OF THE INVENTION A compact, self-contained, transistorizedinstrument primarily utilizing integrated circuits to detect, determine,and display the pulse propigation time from the heart to an extremity,typically a finger or toe, in an individual. The present invention maybe used with its own peripheral pulse and electrocardiogram detectorsand amplifiers, or it may be used with external peripheral pulse andelectrocardiogram detectors and amplifiers.

The present invention detects each cardiac ventricular contraction(systole) from the electrocardiogram,

and the succeeding peripheral pulse from a pulse detector strapped to afinger or toe. Each timing cycle is initiated by a cardiac ventricularcontraction and ended by the succeeding peripheral pulse. Upon thecompletion of the timing cycle, the elapsed time, in hundredths of asecond, is immediately displayed on a milliammeter. When the next timingcycle is completed, its duration is immediately displayed on themilliammeter.

The present invention is battery powered, typically nickel-cadmium,rechargable batteries are used, provides a meter readout of the hoursuse remaining, and has its own recharging circuit so recharging may beaccomplished from any standard volt A.C. electrical outlet.

OBJECTS OF THE INVENTION It is therefore an object of this invention toprovide a monitor to detect, determine, and display the pulsepropigation time from the heart to an extremity, typically a finger ortoe, in hundredths of a second.

A further object of the present invention is to provide the pulsepropigation time on a continuous, real time basis.

A further object of the present invention is to provide a monitor whichis portable, compact, lightweight, and which does not require theservices of highly skilled personel during the operation thereof.

A further object of the present invention is to provide a completelydependable and reliable automatic pulse propigation time monitor.

A further object of the present invention is to provide for an entirelytransistorized pulse propigation time monitor, primarily usingintegrated circuits.

A further object of the present invention is to provide thedetermination and display of the pulse propigation time without its ownperipheral pulse and electrocardiogram detectors and amplifiers; whenconnected to standard peripheral pulse and electrocardiogram detectorsand amplifiers via the external peripheral pulse and electrocardiograminputs.

DESCRIPTION OF THE DRAWINGS Other objects and advantages of the presentinvention will become apparent from the following detailed descriptionof the preferred embodiment thereof, when considered in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagrammatic representation of a preferred embodimentof a pulse propigation time detecting, determining, and displayingdevice in accordance with the present invention during utilization by apatient; and

FIG. 2 is an embodiment in which the pulse propigation time monitor isportable and self-contained.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pulse propigation time fromthe heart to an extremity, typically a finger or toe, is an importantmeasure of a patients cardiac, vascular, and blood volume status. Itconsists of the time required for ventricular depolarization, the timefor isometric contraction of the ventricle, and the time fortransmission of the arterial pressure wave from the aortic valve to thepoint of pulse detection on the extremity.

It has been shown that the time it takes for a pulse wave to travel froma patients heart to his finger becomes prolonged during anesthesiabefore there is any change in his blood pressure, pulse rate, orelectrocardiogram. Some of the prolongation is due to an increasedisometric contraction interval, but most of the delay is attributed to adecreased transmission of the pulse wave in the aorta and arteries. Ithas also been shown that a decrease in cardiac output can slow thearterial pressure wave.

From this it is assumed that the prolongation of the pulse propigationtime is caused by both a decrease in myocardial contractility and adecrease in cardiac output. The present invention therefore provides amethod of earlier detection of cardiovascular depression by noninvasivemeans than ever possible before.

All that is required for the present invention to function is to strapthe peripheral arterial pulse detector on the distal phalanx of a fingeror toe, and to tape three silver-silver chloride electrodes to which astandard conductive paste has been applied to the patients skin whichhas been cleaned. The two detecting electrodes are placed as far fromthe heart and from each other as possible, typically one electrode oneach arm. The third electrode connects the patient to the circuit groundand may be applied to any convenient spot on the patients body. Fromthis it can be seen that the use of the present invention does notrequire personnel with any special training or knowledge.

The present invention will now be described in detail with particularreference to FIG. 1, showing the diagrammatic representation of thepreferred embodiment.

The apparatus of the present invention utilizes the technique ofapplying a sensor to the distal phalanx of the patients finger 11 todetect the peripheral pulse waveform. The detector is a miniaturesemiconductor strain gauge 13 which is easily applied to the distalphalanx ofa finger 11, employing a Velcro cuff 12. The detector is smallenough X 5 mm.) to be used on newborns as well as adults. The peripheralpulse is de tected by the strain gauge 13 which forms one limb of theWheatstone bridge 14.

The output of strain gauge 13 is an electrical signal that varies inamplitude in proportion to the pressure acting through an artery wall.Since the heart beats, the flow of blood through the arteries isnecessarily pulsating. Therefore the electrical signal detected has asubstantially pulse-like waveform.

Due to unbalance in the Wheatstone bridge 14 caused by the peripheralarterial pulse, a signal is transferred to amplifier 15 to be amplified.The output of amplifier 15 passes through amplifier and filter 16 whichfurther amplifies the signal and removes any 60 Hertz interferencepresent.

The peripheral pulse gain adjustment 45, which is a part of amplifierand filter 16, may be adjusted to provide an adequate signal, afterpassing through the l Hertz low pass filter 18, to trigger the leveldetector 19.

The present invention may be used with currently available peripheralpulse detectors and amplifiers. In this case, the output from a standardperipheral pulse detector and amplifier is fed into the externalperipheral pulse input 17.

The peripheral pulse waveform, either from the amplifier and 60 Hertzfilter 16 or the external peripheral pulse input 17 is then fed to a lowpass (1 Hertz) filter 18 to remove the dicrotic notch caused by aorticvalvular closure, which could cause an abnormal readout of the pulsepropigation time. The signal then triggers a level detector 19 whichprovides a negative step change in voltage. This negative pulse fromlevel detector 19, representing the peripheral pulse waveform, and theend of one timing cycle for the measurement of the pulse propigationtime, then momentarily turns on field effect transistor switch 33.

The apparatus of the present invention utilizes the technique ofapplying two standard silver-silver chloride electrodes 20 filled with astandard conductive paste to two separate points on the patients bodydistant from the heart, typically the patients arms 21, to detect theelectrical activity of the heart (electrocardiogram). A thirdsilver-silver chloride electrode 22 filled with a standard conductivepaste grounds the patient to the circuit ground 23, and may be placedanywhere on the patients skin. The silver-silver chloride electrodes 20and 22 are small enough to be used on newborns as well as adults, andare fastened to the patients body with adhesive tape or any suitableadhesive.

The detected electrocardiogram is fed to amplifier 24 to be amplified.The output of amplifier 24 passes through amplifier and Hertz filter 25which further amplifies the electrocardiogram and removes any 60 Hertzinterference present.

The electrocardiogram gain adjustment 44, which is part of amplifier and60 Hertz filter 25, may be adjusted to provide an adequate signal, afterpassing through the 23 Kilohertz bandpass filter 27, to trigger themonostable multivibrator 28.

The present invention may be used with currently availableelectrocardiogram detectors and amplifiers. In this case, the outputfrom the standard electrocardiogram detector and amplifier is fed intothe external electrocardiogram input 26.

The electrocardiogram, either from the amplifier and 60 Hertz filter 25or the external electrocardiogram input 26 is then fed to a 23 Kilohertzbandpass filter 27 to remove all components of the electrocardiogramexcept the QRS waveform, which represents cardiac ventricularcontraction (systole).

The QRS waveform from 23 Kilohertz bandpass filter 27 then triggersmonostable multivibrator 28 which generates a positive pulse andmomentarily activates reset circuit 29. When activated, the resetcircuit 29 momentarily shorts the timing or sample capacitor 31 toground, resetting sample or timing capacitor 31 to zero volts.

Constant current source 30 provides a source of constant current whichis passed to sample capacitor 31. This provides a linear ramp voltagefrom sample capacitor 31 that is directly proportional to time. In otherwords, when the output from the timing or sample capacitor 31 is 0.1volts in 0.l seconds, it will be 0.2 volts in 0.2 seconds, 0.3 volts in0.3 seconds, and so on.

Meter protective circuit 32 limits the maximum voltage output fromsample capacitor 31 so that meter readout of pulse propigation time 37cannot be overloaded if the sample capacitor 31 is not reset to zerovolts periodically by reset circuit 29.

Field effect transistor switch 33 is normally off; when it ismomentarily turned on by level detector 19, it allows the voltage onsample timing or capacitor 31 to be transferred to hold capacitor 34.This voltage on hold capacitor 34 then remains constant due tooperational amplifier buffer 35 until the field effect transistor switch33 is again turned on, at which time a new voltage on sample capacitor31 is transferred to hold capacitor 34.

Calibrate adjustment 36 allows the current output from operationalamplifier buffer 35 to be adjusted to the meter used in meter readout ofpulse propigation time 37. Typically a 0 to 1 milliammeter is used inmeter readout of pulse propigation time 37, and is calibrated inhundredths of a second, from 0 to 1 second.

For a constant load, as provided in calibrate adjustment 36, the currentoutput from operational amplifier buffer 35 is directly proportional tothe voltage on hold capacitor 34. In other words, if 100 microamperesfrom calibrate adjustment 36 equals 0.1 volts on hold capacitor 34,then200 microamperes from calibrate adjustment 36 will equal 0.2 voltson hold capacitor 34, 3011 microamperes from calibrate adjustment 36will equal 0.3 volts on hold capacitor 34, and so on.

In summary, the voltage on sample capacitor 31 is directly proportionalto time. This voltage on sample capacitor 31 is transferred to holdcapacitor 34 via field effect transistor switch 33 and is stillproportional to time. The voltage on hold capacitor 34 is directlyproportional to the current output from calibrate adjustment 36.Therefore the current output from calibrate adjustment 36 is directlyproportional to time.

The calibrate adjustment 36 is set so that, after sample capacitor 31 isreset to zero volts, the milliammeter in meter readout of pulsepropigation time 37 will read one second (full scale) when the fieldeffect transistor switch 33 is momentarily turned on one second later.

From the above, it can be seen that the pulse propigation time ismeasured by the QRS complex from the electrocardiogram causing thesample capacitor 31 to be reset to zero volts and then the peripheralpulse waveform causing the field effect transistor switch 33 tomomentarily be turned on and transfer a voltage proportional to timefrom sample capacitor 31 to hold capacitor 34. This voltage drivesoperational amplifier buffer 35 and is read out in hundredths of asecond on the milliammeter in meter readout of pulse propigation time37.

Following the momentary turning on of the field effect transistor switch33 by the peripheral pulse, the sample capacitor 31 is again reset tozero volts by the next QRS complex, and a new timing cycle begins. Thenext peripheral pulse again momentarily turns on field effect transistorswitch 33 and a new voltage representing the new ventricular to fingerpulse propigation time is transferred to hold capacitor 34, which, inturn, is read out in hundredths of a second of the milliammeter in themeter readout of pulse propigation time 37.

The battery charge indicator circuit 39 is a series pass transistorcircuit driven by the +12 volt battery 40 and adjusted to turn off whenthe output from the +12 volt battery 40 drops to volts. The batterycharge indicator circuit 39 drives a microammeter, typically 0 to 500microamperes, in the meter readout of battery charge 38, and is set sothe microammeter reads full scale with a full battery charge on the +12volt battery 40. The microammeter is calibrated in hours of battery useleft, and therefore tells how long the present invention may be used,and when its power supply needs recharging.

The electronic circuitry in the apparatus described above is entirelysolid state, primarily utilizes integrated circuit operationalamplifiers, is powered by a +12 volt and a 6 volt DC. power supply,typically a +12 volt battery 41) and a -6 volt battery 41, and may becontained in one compact unit 43, as shown in FIG. 2. The +12 voltbattery 40 and 6 volt battery 41 are typically nickel-cadmium, andincluded in the unit 43.

The +12 volt battery 40 and 6 volt battery 41 supply the positive andnegative power supplies for the integrated circuit operationalamplifiers. The Wheatstone bridge 14, which includes the semiconductorstrain gauge 13, is powered by the -6 volt batter 41. The constantcurrent source 31), 23 Kilohertz bandpass filter 27, and battery chargeindicator circuit 39, are powered by the +12 volt battery 41).

A battery recharging circuit 42, contained in the unit 43, steps down,rectifies, and limits the volts A.C. available from any standardelectrical outlet to the proper D.C. voltages and currents to rechargethe +12 volt battery 41) and 6 volt battery 41, typically nickelcadmiumbatteries, which power the electronic circuitry. The recharging is donewhen the function switch 48 is in the off position, and is accomplishedby connecting the recharging input 46 to any 120 volt A.C. outlet. Whenrecharging is occurring, indicator lamp 47 is on.

It will be appreciated that my invention provides equipment formeasuring and displaying the time lapse between a heartbeat and acorresponding peripheral arterial pulse, comprising: A. a timing orsample capacitor 31 for accumulating voltage on a linear basis whenreset by a voltage discharge operation at the start of a timing cycle;B. an apparatus 20-25 and 27 or 26-27 for detecting the electricalactivity characterizing the cardiac ventricular contraction of aheartbeat and for producing an electrical QRS signal corresponding tothe QRS waveform content of said electrical activity; C. means 28-29responsive to said QRS signal for resetting said timing capacitor tostart a timing cycle; D. a current source 311 for charging said timingcapacitor 31 during said timing cycle with a voltage which is directlyproportional to the elapsed time; E. sensing and generating meansincluding an arterial pulse detector 13 for sensing, at the end of saidtiming cycle, a peripheral arterial pulse corresponding to saidheartbeat, and generating means, including either 14-16 and 18-19 or17-19, for producing an electrical signal corresponding to said sensedpulse; and F. measuring and signaling means 33-37 operative, at the endof said timing cycle, in response to said electrical pulse-correspondingsignal, to measure the time-proportional voltage of (or a correspondingvoltage transferred from) said timing capacitor and to signal thatmeasurement in terms of elapsed time. The QRS signal resets the timingcycle by resetting the timing capacitor 31 to zero volts. The measuringand signaling means includes a hold capacitor 34 and a normally openelectrical switch 33 operative, when closed, to interconnect said timingand hold capacitors while said electrical pulse-corresponding signalends the timing cycle by normally closing the normally open switch 33 tocharge the hold capacitor 34 with a time-proportional voltage from thetiming capacitor 31. Also, the measuring and signaling means includes avisual display device (meter 37) for providing an instantaneous read-outof the voltage on the hold capacitor 34 in terms of the elapsed timebetween the start and end of said timing cycle.

The present invention provides an instantaneous readout of the pulsepropigation time, in hundredths of a second, from the heart to anextremity, typically a finger or toe. That is, the QRS complex initiatesa timing cycle when it resets the sample capacitor 31 to zero volts, andthe peripheral pulse waveform ends the timing cycle when it momentarilyturns on the field effect transistor switch 33, causing an instantaneousreadout of the pulse propigation time from the heart to a finger or toeon meter readout of pulse propigation time 37. This readout is displayedin hundredths of a second until the next timing cycle is completed, atwhich time it is displayed.

The information provided by the present invention, i.e., the pulsepropigation time from the heart to a point on an extremity, typically afinger or toe, is obtained by a noninvasive means to the individualbeing monitored. That is, only surface detectors and electrodes areused. This has never been accomplished before.

If desired, the present invention can utilize the signals from standardperipheral pulse and electrocardiogram detectors and amplifiers toprovide the pulse propigation time from the heart to a point on anextremity, typically a finger or toe. From this it is obvious that thepresent invention could be made in a form lacking its own peripheralpulse and electrocardiogram detectors and amplifiers, but provide thesame information when used in conjunction with the above said standarddetectors and amplifiers.

The present invention is compact, lightweight, entirely solid state, hasits own self-contained, rechargable battery supply, operates for a longperiod of time before recharging is necessary, has an extremely shortwarm up time of 2 or 3 seconds, and may be used in a remote area. Thepresent invention can be easily mounted on an anesthesia machine, shelf,or intravenous pole in the operating room. It is a valuable adjunct tothe evaluation of a patients cardiovascular status at any time; duringan anesthetic or surgery, in the clinical evaluation of a patientscardiovascular status, or during a life threatening illness as amyocardial infarction. Because of its noninvasive means of detection,the patient is not subjected to any stress to obtain the information,and no special knowledge, skill, or training is required to utilize thepresent invention.

()bviously many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore understoodthat within the scope of the appended claims the invention may bepracticed otherwise than as specifically described.

What is claimed and desired to be secured by letters patent of theUnited States is:

1. Equipment for measuring and displaying the time lapse between a givenheartbeat and the corresponding arterial pulse at a peripheral area ofthe body of a patient, comprising:

A. a sample capacitor capable of accumulating voltage on a linear basisand operative, when reset by a voltage discharge operation, to start agiven timing cycle;

B. a heartbeat-actuated capacitor-resetting apparatus for dischargingand resetting said sample capacitor to start a given timing cycle, saidapparatus producing an electrical signal representative of the QRSwaveform content of a given heartbeat, said apparatus including 1. anECG apparatus for detecting the electrical activity, which characterizesthe cardiac ventricular contraction of said given heartbeat and forproducing an electrical input signal representative of such electricalactivity,

2. a bandpass filter connected to said ECG apparatus and operative toremove substantially all components of said input signal except the QRSwaveform,

3. a monostable multivibrator connected to receive said QRS waveformfrom said bandpass filter and operative, in response thereto, to providea step change in voltage, and

4. a reset circuit connecting said sample capacitor to said monostablemultivibrator and operative momentarily, in response to saidmultivibrator voltage change, to discharge said capacitor and thus resetit for the start of said given timing cycle;

C. constant current supply and protective circuit means including 1. aconstant current source connected to said sample capacitor for chargingit during said given timing cycle with a voltage which is directlyproportional to the elapsed time, and

2. a protective circuit connected to said sample capacitor and operativeto limit its accumulation of voltage upon a failure to reset the samplecapaci- 2 tor at the end of said given timing cycle;

D. a field effect transistor switch connected to said sample capacitor,said switch normally being biased off;

E. pulse-actuated means for ending said given timing cycle bymomentarily turning said field effect transistor switch on, said meansincluding 1. a peripheral-pulse detection apparatus for producing anelectrical peripheral pulse input signal which is representative of thearterial pulse corresponding to said given heartbeat,

2. a low pass filter connected to said peripheralpulse-apparatus forreceiving and modifying said peripheral-pulse input signal by removing,from it, the dicrotic notch characteristic of a peripheral pulsewaveform, and

3. a level detector connected to said low pass filter and to said fieldeffect transistor switch and operative, in response to said modifiedperipheral pulse input signal, to provide a step change in the voltagewhich turns said transistor switch on momentarily; and

F. means for displaying a time lapse readout, corresponding to thelinear voltage which accumulated on the sample capacitor during saidgiven timing cycle, said means including 1. a hold capacitor connectedto said field effect transistor switch and operative, when saidtransistor switch is momentarily turned on, to be charged with a voltagecorresponding to the voltage which accumulated on said sample capacitorduring said time lapse,

2. an operational amplifier buffer connected to said hold capacitor tomaintain the voltage charge on said hold capacitor at a constant valueand to provide a current output directly proportional thereto,

3. a meter for receiving an electrical input current and providing avisual time readout which is directly proportional to the input currentit receives, and

4. a calibrate adjustment connected to the buffer and the meter toprovide the meter with input current directly proportional to theelapsed heartbeat-to-pulse time.

l k k k

1. Equipment for measuring and displaying the time lapse between a givenheartbeat and the corresponding arterial pulse at a peripheral area ofthe body of a patient, comprising: A. a sample capacitor capable ofaccumulating voltage on a linear basis and operative, when reset by avoltage discharge operation, to start a given timing cycle; B. aheartbeat-actuated capacitor-resetting apparatus for discharging andresetting said sample capacitor to start a given timing cycle, saidapparatus producing an electrical signal representative of the QRSwaveform content of a given heartbeat, said apparatus including
 1. anECG apparatus for detecting the electrical activity, which characterizesthe cardiac ventricular contraction of said given heartbeat and forproducing an electrical input signal representative of such electricalactivity,
 2. a bandpass filter connected to said ECG apparatus andoperative to remove substantially all components of said input signalexcept the QRS waveform,
 3. a monostable multivibrator connected toreceive said QRS waveform from said bandpass filter and operative, inresponse thereto, to provide a step change in voltage, and
 4. a resetcircuit connecting said sample capacitor to said monostablemultivibrator and operative momentarily, in response to saidmultivibrator voltage change, to discharge said capacitor and thus resetit for the start of said given timing cycle; C. constant current supplyand protective circuit means including
 1. a constant current sourceconnected to said sample capacitor for charging it during said giventiming cycle with a voltage which is directly proportional to theelapsed time, and
 2. a protective circuit connected to said samplecapacitor and operative to limit its accumulation of voltage upon afailure to reset the sample capacitor at the end of said given timingcycle; D. a field effect transistor switch connected to said samplecapacitor, said switch normally being biased off; E. pulse-actuatedmeans for ending said given timing cycle by momentarily turning saidfield effect transistor switch on, said means including
 1. aperipheral-pulse detection apparatus for producing an electricalperipheral pulse input signal which is representative of the arterialpulse corresponding to said given heartbeat,
 2. a low pass filterconnected to said peripheral-pulseapparatus for receiving and modifyingsaid peripheral-pulse input signal by removing, from it, the dicroticnotch characteristic of a peripheral pulse waveform, and
 3. a leveldetector connected to said low pass filter and to said field effecttransistor switch and operative, in response to said modified peripheralpulse input signal, to provide a step change in the voltage which turnssaid transistor switch on momentarily; and F. means for displaying atime lapse readout, corresponding to the linear voltage whichaccumulated on the sample capacitor during said given timing cycle, saidmeans including
 1. a hold capacitor connected to said field effecttransistor switch and operative, when said transistor switch ismomentarily turned on, to be charged with a voltage corresponding to thevoltage which accumulated on said sample capacitor during said timelapse,
 2. an operational amplifier buffer connected to said holdcapacitor to maintain the voltage charge on said hold capacitor at aconstant value and to provide a current output directly proportionalthereto,
 3. a meter for receiving an electrical input current andproviding a vIsual time readout which is directly proportional to theinput current it receives, and
 4. a calibrate adjustment connected tothe buffer and the meter to provide the meter with input currentdirectly proportional to the elapsed heartbeat-to-pulse time.
 2. abandpass filter connected to said ECG apparatus and operative to removesubstantially all components of said input signal except the QRSwaveform,
 2. an operational amplifier buffer connected to said holdcapacitor to maintain the voltage charge on said hold capacitor at aconstant value and to provide a current output directly proportionalthereto,
 2. a low pass filter connected to saidperipheral-pulse-apparatus for receiving and modifying saidperipheral-pulse input signal by removing, from it, the dicrotic notchcharacteristic of a peripheral pulse waveform, and
 2. a protectivecircuit connected to said sample capacitor and operative to limit itsaccumulation of voltage upon a failure to reset the sample capacitor atthe end of said given timing cycle; D. a field effect transistor switchconnected to said sample capacitor, said switch normally being biasedoff; E. pulse-actuated means for ending said given timing cycle bymomentarily turning said field effect transistor switch on, said meansincluding
 3. a level detector connected to said low pass filter and tosaid field effect transistor switch and operative, in response to saidmodified peripheral pulse input signal, to provide a step change in thevoltage which turns said transistor switch on momentarily; and F. meansfor displaying a time lapse readout, corresponding to the linear voltagewhich accumulated on the sample capacitor during said given timingcycle, said means including
 3. a monostable multivibrator connected toreceive said QRS waveform from said bandpass filter and operative, inresponse thereto, to provide a step change in voltage, and
 3. a meterfor receiving an electrical input current and providing a vIsual timereadout which is directly proportional to the input current it receives,and
 4. a reset circuit connecting said sample capacitor to saidmonostable multivibrator and operative momentarily, in response to saidmultivibrator voltage change, to discharge said capacitor and thus resetit for the start of said given timing cycle; C. constant current supplyand protective circuit means including
 4. a calibrate adjustmentconnected to the buffer and the meter to provide the meter with inputcurrent directly proportional to the elapsed heartbeat-to-pulse time.